LightSail Missions of The Planetary Society
LightSail-A is a nanosatellite (a triple CubeSat configuration) project of TPS (The Planetary Society) of Pasadena, CA, USA. The objective is to demonstrate solar sail technology in a spaceborne mission (test of sail deployment and controlled flight).
LightSail-A will have four triangular sails, arranged in a diamond shape resembling a giant kite. Constructed of 32 m2 of mylar, LightSail-A will be placed into an orbital altitude of over (originally intended 800 km), high enough to escape the drag of Earth's uppermost atmosphere. At that altitude the spacecraft will be subject only to the force of gravity keeping it in orbit and the pressure of sunlight on its sails increasing the orbital energy. The mission will give us a good, clean trial of sunlight as a means of propulsion. 1) 2)
Figure 1: Artist's rendition of the deployed LightSail-A mission (image credit: Planetary Society)
Some background: On June 21, 2005, The Planetary Society tried to send its first solar sail, Cosmos 1, into orbit but failed because the Volna rocket it was riding didn't reach the needed orbital altitude. Later on, the Planetary Society took over NASA's small project called NanoSail-D, which they renamed to LightSail-1. The NanoSail-D mission had also failed to attain orbit due to the failure of its Falcon 1 launch vehicle in August 2008. The LightSail-A project was announced by the Planetary Society in November 2009. The project is privately financed. 3)
LightSail-A is technically more ambitious mission than the NanoSail-D mission of NASA, both because of its lower mass/area ratio (140 versus 300 gram/m2), and because it has attitude control equipment that will allow it to maintain a commanded orientation relative to the sun, and hence will be able to produce a deliberately-directed solar sailing thrust force.
In June 2010, the LightSail-A nanosatellite project passed its CDR (Critical Design Review).
On March 11, 2011, the Planetary Society conducted the first full scale deployment of the LightSail-A solar sail at Stellar Exploration in San Luis Obispo, California.
LightSail is a citizen-funded project by The Planetary Society, the world's largest non-profit space advocacy group. Two small spacecraft will be sent into Earth orbit carrying large, reflective sails measuring 32 m2 . The first mission is a May 2015 test flight that will pave the way for a second, full-fledged solar sailing demonstration in 2016. LightSail-A will demonstrate the deployment of a 32 m2 solar sail from a 3U CubeSat platform. 4)
SLR (Satellite Laser Ranging) will be utilized to perform spacecraft orbit determination before and after solar sail deployment. Without an onboard GPS receiver, SLR is the primary orbit determination method.
The LightSail-A spacecraft is a 3U CubeSat (or triple CubeSat) with a mass of ~ 4.9 kg and a size of 340 mm x 100 mm x 100 mm; it was built by Ecliptic Enterprises Corporation, California Polytechnic University San Luis Obispo, Georgia Institute of Technology, Boreal Space, Half-Band Technologies LLC and Stellar Exploration, Inc.
The CubeSat platform is provided by CalPoly. One unit of the CubeSat is being used for the central electronics and the control module, while the other 2 units of the CubeSat will contain the payload, i.e. the solar sail module. Cameras, additional sensors, and a control system will be added to the basic CubeSat electronics bus. The function of the cameras is to verify the deployment of the solar sail. 5) 6) 7) 8) 9)
LightSail-A is being developed largely as a technology demonstrator for the sail deployment and control mechanisms. Following launch, Lightsail-A will conduct a several week mission during which it will deploy its sail and undertake a series of controlled maneuvers. By manipulating the orientation of the sail with respect to the sun, the force of the solar radiation against the sail can be controlled which will ultimately result in a measurable change in the satellite's orbit.
Figure 2: Schematic view of the LightSail-A nanosatellite (image credit: The Planetary Society)
The LightSail-A spacecraft features (Ref. 7):
- 10 solar panels -- four deployable arrays with panels on each side plus one panel on the top and one on the bottom of the spacecraft
- Two 2 Mpixel cameras mounted at the end of two of the solar panels (only one camera is visible in Figure 3)
- Four sun sensors mounted at the end of four of the solar panels
- Six tiny ultra-sensitive accelerometers that will provide a direct measure of the light-force
- A momentum wheel for attitude control (colored red in Figure 3)
- Three single axis gyros (yellow)
- Three torque rods (gray) also part of the attitude control system
- A battery (salmon-colored, looking like a laptop computer battery).
Figure 3: Alternate view of the LighSail1-1 nanosatellite (image credit: The Planetary Society)
Below the empty space in Figure 3, where the solar sail is stowed for launch, there are four new deployer mechanisms, invented by the project team, around which the TRAC (Triangular Rollable and Collapsible) booms are wound. The sails themselves consist of mylar film with 4.5 µm in thickness, aluminized and seamed for rip-stop protection: the thinnest sail so far made for spaceflight. When deployed, it provides a total area of 32 m2 (size of 5.6 m x 5.6 m). The TRAC booms were developed at AFRL (Air Force Research Laboratory). 10)
The avionics assembly is located at the top of the nanosatellite bus in Figure 3, consisting of the command, control and data handling circuit board, the payload interface board, the radio transceiver, and the power regulator.
A whip antenna is mounted at the bottom of of the nanosatellite bus in Figure 3, providing UHF communications to the ground segment (435 MHz in uplink and downlink).
ADCS (Attitude Determination and Control Subsystem) modes:
• B-dot detumble (only sensors used are the magnetometers)
• Momentum wheel turn-on
• Orbit raising (thrust on/thrust off).
The ADCS monitors and controls LightSail attitude and body rates. It detumbles the stowed spacecraft after P-POD deployment from a maximum 25 º/s tipoff rate in any axis to 2-10º/s. It performs a coarse alignment of the RF antenna on the +Z axis of the spacecraft with the Earth's magnetic field with maximum variation, once settled, of <60°, which is sufficient for ground communication. After sail deployment, ADCS detumbles the spacecraft from up to 10º/s in any axis to ~2-5º/s.
The momentum wheel is a reaction wheel assembly provided by Sinclair Interplanetary of Toronto, Canada (heritage of the CanX-2 mission of UTIAS/SFL). The nominal momentum is 0.060 Nms; an angular velocity of 2.5º/s is provided.
Figure 4: Photo of the reaction wheel assembly (image credit: Sinclair Interplanetary)
The ADCS hardware was sized for significantly varying moments of inertia (for the stowed and deployed configurations). Based on ADCS simulations conducted during 2014, a decision was made to modify the torquer control method to allow for proportional control vs. simple ON/OFF (Bang-Bang) control, deemed to be too abrupt in the stowed configuration. Proportional control was judged to be essential for fine attitude control during the planned LightSail-B solar sailing demonstration phase.
ADCS modeling and simulation results for LightSail-A highlight the expected performance (Figure 6). The orbit was propagated using two-body dynamics with a simple magnetic dipole model for the Earth's magnetic field. Tuning parameters include control frequency (limited by the non-rigid configuration with the sails deployed), duty cycle, and torque rod dipole. Initial conditions were varied to analyze settling time and stability. Perturbations included magnetometer and torque rod axis misalignments, aerodynamic torque, solar radiation pressure torque, and gravity gradient torque.
Table 1 summarizes the sensors and actuators supporting the LightSail ADCS.
Table 1: ADCS sensors and actuators
The LightSail-B mission includes a momentum wheel that aids in solar sail maneuvers on orbit to demonstrate an orbital inclination change, per an ADCS concept articulated in 2013. 11) The simulation for these operations has been developed and is shown in Figure 5.
Figure 5: Simulink model for LightSail-B orbital inclination change (image credit: Planetary Society, LightSail Team)
Figure 6: ADCS detumble simulation results (image credit: Planetary Society, LightSail Team)
Figure 7: LightSail team members Alex Diaz (left) and Riki Munakata prepare the spacecraft for a sail deployment test (image credit: The Planetary Society) 12)
Figure 8: Illustration of LightSail-A components and subsystems (image credit: Planetary Society, LightSail Team)
EPS (Electrical Power Subsystem): The EPS is composed of the solar arrays, batteries, power distribution, and fault protection circuitry. In full Sun, the four long solar panels generate a maximum 6 W of power each with the two shorter panels providing 2 W each. Solar power is routed through the main avionics board and charges a set of 8 lithium-polymer batteries providing power during eclipse periods. Each battery cell has its own charge monitoring/protection circuit and ties individually to the spacecraft bus (VBUS). Each cell monitor independently provides overvoltage and undervoltage protection as well as overcurrent and short-circuit protection to that cell.
The main avionics board contains a low state-of-charge recovery system that initiates when VBUS drops below a specified threshold. Figure 9 summarizes the various battery fault-protection mechanisms, which are more complex.
Power analyses were conducted prior to the LightSail-A mission using the following modes: Detumble, Magnetic Pointing, Deploy Sail and Image, and Downlink. Depth of discharge values were analyzed for all modes, with a maximum (worst-case) of 15% in the Deploy Sail and Image mode.
Figure 9: Battery fault protection mechanisms (image credit: Planetary Society, LightSail Team)
Thermal Subsystem: Temperature sensors are installed on each of the four deployable solar panels, in both cameras, and in the primary avionics board. Solar panel temperature sensors inform the ambient environment of the stowed and deployed solar panels through telemetry. Both LightSail cameras are mounted at the ends of their respective solar panels and, after panel deployment, are subject to temperatures as low as –55ºC during orbital eclipse periods. The cameras require an operating range from 0ºC to 70ºC. A heater is installed in series with a thermostat set to trip ON if the camera temperature falls below 0ºC. The FSW (Flight Software) turns OFF the camera if the operating temperature climbs above 70ºC. Avionics board temperatures are relayed in beacon telemetry.
Avionics and RF Subsystem: The primary avionics board is a Tyvak Intrepid computer board (version 6), which is Atmel-based and hosts a Linux operating system. Integrated onto this main board onto a separate daughterboard is an AX5042 UHF radio transceiver with an operating frequency of 437.435 MHz.
Besides the temperature sensors, the spacecraft also have Sun sensors at the tips of each deployable solar panel and magnetometers near each tip, and gyros measuring X-, Y- and Z-axis rates in the avionics bay.
Table 2: Mission parameters of LightSail-A (Ref. 4)
Figure 10: Overall LightSail architecture - the four deployable solar panels not shown (image credit: LightSail Team, Ref. 40)
Launch: The LightSail-A nanosatellite was launched on May 20, 2015 (15:05:00 UTC) as a secondary payload on an Atlas-5 -501 EELV (Evolved Expendable Launch Vehicle) of ULA from the Cape Canaveral Air Force Station (SLC-41) in Florida. The primary mission was the AFSPC-5 (Air Force Space Command -5) mission -referring to the Boeing built X-37B spaceplane of the USAF into LEO. The X-37B is an unmanned reusable mini shuttle, also known as the OTV (Orbital Test Vehicle) and is flying on the OTV-4 mission. It launches vertically like a satellite but lands horizontally like an airplane. The X-37B mission is testing an electric Hall Effect thruster in its small payload bay, which will be used on future US Air Force satellites. 13) 14)
This Atlas-5 mission also includes the ABC (Aft Bulkhead Carrier) carrying the NRO's (National Reconnaissance Office's) Ultra Lightweight Technology and Research Auxiliary Satellite (ULTRASat).
The 2015 test flight will not carry the spacecraft high enough to escape Earth's atmospheric drag, and will thus not demonstrate controlled solar sailing. Once in orbit, the spacecraft will go through a checkout and testing period of about four weeks before deploying its solar sails. After the sails unfurl, LightSail will test its attitude control system and study the behavior of the sails for a few days before it is pulled back into the planet's atmosphere. Key images and data on the spacecraft's performance will be sent to ground stations at Cal Poly San Luis Obispo and Georgia Tech.
- Initially, a launch of LightSail-A as a secondary payload was manifested on the NPP (NPOESS Preparatory) mission of NASA. However, the LightSail-A project wasn't ready for the launch in October 2011. 15)
- Fall 2012: The Planetary Society has completed the development, manufacture, integration and test of the LightSail spacecraft and placed it into sealed storage awaiting a launch opportunity for flight to medium Earth orbit. LightSail has been designated for flight in NASA's ELaNa (Education Launch of Nanosats) program for over a year. However, no opportunity for a secondary payload flight to medium-Earth orbit (above ~ 800 km), where light pressure will dominate atmospheric drag, has yet been identified. 16)
The Atlas V sent the U.S. Air Force's X-37B space plane on its fourth mission, which also is carrying NASA's METIS (Materials Exposure and Technology Innovation in Space) investigation that will expose about 100 different materials samples to the space environment for more than 200 days. 17) 18) 19)
ELaNa-XI CubeSats: NASA will enable the launch of a small research satellite, or CubeSat, for The Planetary Society in Pasadena, California, as part of the eleventh installment of the Educational Launch of Nanosatellite (ELaNa) mission. The LightSail CubeSat is included as part of an auxiliary payload of 10 CubeSats on the upper stage of the Atlas V rocket that will launch the U.S. Air Force X-37B space plane's fourth mission, scheduled to lift off May 20 from Cape Canaveral Air Force Station, Florida. 20)
The upper stage of the Atlas-5 included the National Reconnaissance Office's third auxiliary mission to launch CubeSats. The ULTRASat (Ultra Lightweight Technology and Research Auxiliary Satellite) carried 10 CubeSats — including LightSail — from five organizations. It was made possible through agreements between NASA, the Air Force's Space and Missile Systems Center and the NRO (National Reconnaissance Office) to work together on CubeSat integration and launch opportunities. 21)
• LightSail-A, a 3U CubeSat of The Planetary Society, Pasadena, CA.
• USS (Unix Space Server) Langley, a 3U CubeSat of the USNA (U.S. Naval Academy) Annapolis, MD. USS Langley is a proof-of-concept mission for providing global Internet access via a nanosatellite constellation. The USS Langley satellite uses a 3U CubeSat bus procured from Pumpkin Inc. under the Colony-1 program of the National Reconnaissance Office.
• BRICSat-P (Ballistically Reinforced Communication Satellite-Propulsion Test Unit), a CubeSat of USNA /George Washington. BRICSat-P is a collaborative 1.5U CubeSat mission of USNA, Annapolis, MD, and the George Washington University, Washington DC, USA. The overall objective is to demonstrate on-orbit operation of an electric propulsion system. 22) 23)
• ParkinsonSat, two 1.5U CubeSats of the USNA (United States Naval Academy). PSat (short for ParkinsonSat) employs a two- way communications transponder for relaying remote telemetry, sensor and user data from remote environmental experiments (in the ground segment) or other data sources back to experimenters via a global network of Internet linked volunteer ground stations. The data transponder also includes all telemetry, command and control for a complete CubeSat.
• GEARRS-2 (Globalstar Experiment And Risk Reduction Satellite-2), a 3U CubeSat of NSL (Near Space Launch Inc.). The objective is to demonstrate whether the Globalstar satellite constellation can be used to relay commands and telemetry for a small satellite mission.
• AeroCube-8A and AeroCube-8B, two 1.5U CubeSats of The Aerospace Corporation, El Segundo, CA. The objective is to test the use of carbon nanotubes in spacecraft construction and radiation protection and investigate electric propulsion technologies. Also known as IMPACT, the two satellites are identical and will be deployed together from a single P-POD.
• OptiCube-1, OptiCube-2, OptiCube-3, three 3U CubeSats of Cal Poly of SLO (San Luis Obispo, CA. The goal of the three OptiCubes is to serve as tracking and calibration targets for studying small satellites and debris in orbit.
All CubeSats are integrated into 8 P-PODs (Poly-Picosatellite Orbital Deployers) which are contained in the NPSCuL (Naval Postgraduate School CubeSat Launcher), built by the NPS (Naval Postgraduate School). The NPSCuL together with the 8 P-PODs and 10 CubeSats is referred to as the ULTRASat (Unique Lightweight Technology and Research Auxiliary Satellite), and is attached to the Centaur upper stage's ABC (Aft Bulkhead Carrier). The assembled ULTRASat is shown in Figure 11 the photo below ready for mate to the launch vehicle along with members of the ULTRASat team consisting of NPS, Office of Space Launch (OSL), United Launch Alliance (ULA) and Cal Poly. 24)
Figure 11: Photo of the ULTRASat team members from the institutions: NPS (Naval Postgraduate School), OSL (Office of Space Launch), ULA (United Launch Alliance) and Cal Poly, along with the ULTRASat payload (image credit: CubeSat)
Figure 12: Photo of the ULTRASat payload (image credit: NRO)
Orbit: LightSail-A will be released into an elliptical orbit, altitude of 350 km x 700 km, eccentricity=0.0253 and an inclination of 55º (Ref. 4).
• June 15, 2015: The LightSail-A test mission is officially over. Following a 25-day stay in low-Earth orbit, the spacecraft tumbled back into Earth's atmosphere Sunday afternoon. Orbital models show reentry likely occurred around 17:23 UTC, give or take 10 minutes, near the South Atlantic Ocean. 25)
- The last time LightSail checked in was on June 11at 4:29 UTC. The corresponding beacon packet, which turned out to be the mission's last, displayed a realtime clock value of 1,837,416 seconds—21 days since launch on May 20. The gyroscopes, which were able to capture snapshots of the spacecraft's tumble rate after every reboot, showed LightSail tumbling at 6.7º/s, 2.4º/s, and 0.3 º/s about its X, Y and Z axes. The Z-axis runs lengthwise through the oblong CubeSat; if LightSail were a gigantic top with its sails parallel to the floor, it was hardly spinning at all.
- The day after sail deployment on June 8, LightSail's rotational rate was a leisurely 116 seconds, according to observers using a wide-field survey telescope in Russia. That changed as the spacecraft dipped deeper into the atmosphere. By June 11, the rate had sped up to 36 seconds. On the day before reentry, it was 21 seconds.
Figure 13: LightSail's final moments in space, analyzed by Ted Molczan in great detai (image credit: The Planetary Society) 26)
• June 12, 2015: Since unfurling its solar sails on June 7, the spacecraft has dipped steadily toward Earth as it trawls through the upper atmosphere. It's now in a 330 km xy 523 km orbit — down from a high point of about 700 km. Predictions for reentry continue to converge on Sunday, June 14. It's likely that come Monday morning, LightSail will be no more. 27)
• June 9, 2015: The Planetary Society's LightSail test mission successfully completed its primary objective of deploying a solar sail in low-Earth orbit, mission managers said today. The mission was declared a success by TPS CEO Bill Nye. During a ground station pass over Cal Poly San Luis Obispo that began at 17:26 UTC, the final pieces of an image showcasing LightSail's deployed solar sails were received on Earth. The image confirms the sails have unfurled, which was the final milestone of a shakedown mission designed to pave the way for a full-fledged solar sail flight of LightSail-B in 2016. 28)
- The mission began May 20 with a launch from Cape Canaveral aboard a United Launch Alliance Atlas V rocket. The spacecraft fought its way through software glitches, two signal losses and unexpected battery behavior before finally deploying its solar sails on June 7.
- The LightSail team is now downloading a second camera image from the opposite side of the spacecraft before it reenters Earth's atmosphere. Because LightSail was directly between the sun and Earth at the time of image acquisition on June 8, it is believed the second photograph may include a view of Earth.
- Next, engineers may "walk out" the sail booms to increase the tension on the sails, which could further flatten the wavy appearance of the Mylar. The image also appears slightly distorted due to the camera's fish-eye lens. The team will analyze all sail imagery and any tensioning results in preparation for next year's flight, when LightSail operates in a higher orbit and uses sunlight for propulsion.
Figure 14: First image of the deployed solar sail of the LightSail-A mission (image credit: The Planetary Society)
• June 4, 2015: The LightSail test spacecraft has fallen silent for a second time, less than a day after completing what appeared to be a successful solar panel deployment. Mission managers believe the CubeSat's batteries are in a safe mode-like condition designed to protect the electronics until power levels are safe for operations. 29)
• June 3, 2015 (22:55 UTC): The LightSail test spacecraft didn't send home pretty pictures of Earth today. But it did relay promising signs that its deployable solar panels swung successfully out into space. At about 12:10 UTC, the nickel-chromium burn wire inside LightSail's aft compartment was commanded to heat up and sever the fishing line-like material, holding the spacecraft's four solar panels closed. The panels, attached by hinges to the CubeSat's front end, must be released to clear a path for solar sail deployment. 30)
- LightSail's rotational rate changed, indicating something had happened. But by the time the spacecraft came around the Earth on its next orbit, the telemetry showed it had rebooted, and its power levels were trending lower than expected. Encouragingly, the temperature sensors onboard the solar panels were a chilly -48ºC at reboot time, indicating the panels were no longer pressed against the chassis.
- LightSail's cameras, which are mounted to the ends of two solar panels, also experienced the bitter cold. For protection, they are equipped with automatic heaters, which consume about the same amount of power as leaving the cameras turned on. Because the heating of the burn wire had already depleted some of the spacecraft's batteries, it's possible power levels fell low enough to trigger a failsafe reboot. More analysis, however, is needed to say anything with certainty.
- With battery levels continuing to hover around 3.9 V during subsequent ground passes, the team postponed image acquisition to focus on stabilizing the spacecraft. Ideally, the batteries should be topped off at 4.2 V before proceeding with power-intensive activities, including sail deployment.
- Engineers also saw a third data point to indicate the solar panels were open. The spacecraft's sun sensors normally show 90º offsets due to their positions along all four solar panels. After the panel deployment command was issued, the offset angles increased, consistent with the panels rotating into angled positions. (The panels do not flip a full 180º after deployment.)
- The spacecraft is out of range until June 4 (Thursday), with the next ground station pass expected to begin at 8:45 UTC. A team meeting is scheduled to discuss the latest telemetry data. With evidence mounting in favor of a successful panel deployment, and an itch to press forward on the solar sails as soon as possible, further test imaging may be scrapped. Providing battery levels return to normal, and any outstanding issues are resolved, a June 5 (Friday) deployment could still be in the works.
• June 3, 2015: LightSail Mission Managers have split the spacecraft's sail deployment sequence into two segments, following an extended camera checkout period that wrapped up June 2. On June 3 (Wednesday), the CubeSat's deployable solar panels will be released, followed by an additional imaging session to verify all systems are go for sail deployment. The deployment itself is now targeted for the morning of June 5 (Friday), during a ground station pass that begins at 16:47 UTC. 31)
- When LightSail reached orbit, its solar panel deployment switches had been triggered, indicating the panels were possibly ajar or deployed. The four hinged panels are designed to open outward, clearing a path for solar sail deployment and positioning the onboard cameras for imaging.
• June 2, 2015: The first image has finished downloading! 32)
Figure 15: This image of LightSail's aft compartment was captured by one of the spacecraft's two onboard cameras. The cameras, which are mounted to two of the four deployable solar panels, face inward until sail deployment, when they hinge outward. The wheel in the center top of the image is part of the sail deployment motor (image credit: The Planetary Society)
• May 31,2015: The LightSail test spacecraft reported for duty this afternoon, heralding the end of an uneasy silence caused by a suspected software glitch. At 21:21 UTC, an automated radio chirp was received and decoded at the spacecraft's Cal Poly San Luis Obispo ground station. Another came in eight minutes later. The real-time clock on board the spacecraft, which does not reset after a software reboot, read 908,125 seconds — approximately ten-and-a-half days since LightSail's May 20 launch. 33)
- "Based upon the on-board timers contained within the beacon (and comparing them to beacons following deployment), it appears that a reboot occurred within the past day," wrote Georgia Tech professor David Spencer, LightSail's mission manager. "Due to uncertainty in the orbit state (TLEs), our ability to reliably track the spacecraft is marginal at this point. Cal Poly is coordinating with international colleagues to arrange their support in acquiring beacon telemetry," he said.
- LightSail is not out of the woods yet. Its exact position remains fuzzy, complicating two-way communication. Today's contact marks the first time engineers can compare the spacecraft's signal with orbital models called TLEs (Two-Line Element) sets. There are ten TLEs associated with the ULTRASat fleet that joined LightSail for a free ride to orbit courtesy of a ULA (United Launch Alliance) Atlas V rocket. Which TLE represents LightSail is unknown, but each radio chirp's Doppler shift helps narrow down the possibilities.
• May 26, 2015: The Planetary Society's LightSail test mission is paused while engineers wait out a suspected software glitch that has silenced the solar sailing spacecraft. Following a successful start to the mission on May 20, LightSail spent more than two days sending about 140 data packets back to Earth. 34)
- As of May 22, LightSail was continuing to operate normally. The spacecraft's ground stations at Cal Poly San Luis Obispo and Georgia Tech were receiving data on each pass. Power and temperature readings were trending stably, and the spacecraft was in good health.
- But inside the spacecraft's Linux-based flight software, a problem was brewing. Every 15 seconds, LightSail transmits a telemetry beacon packet. The software controlling the main system board writes corresponding information to a file called beacon.csv. If you're not familiar with CSV files, you can think of them as simplified spreadsheets—in fact, most can be opened with Microsoft Excel.
- As more beacons are transmitted, the file grows in size. When it reaches 32 MB — roughly the size of ten compressed music files — it can crash the flight system. The manufacturer of the avionics board corrected this glitch in later software revisions. But alas, LightSail's software version doesn't include the update.
- An the evening of May 22, the team received a heads-up warning them of the vulnerability. A fix was quickly devised to prevent the spacecraft from crashing, and it was scheduled to be uploaded during the next ground station pass. But before that happened, LightSail fell silent. The last data packet received from the spacecraft was May 22 at 21:31 UTC.
- LightSail is likely now frozen, not unlike the way a desktop computer suddenly stops responding. A reboot should clear the contents of the problematic beacon.csv file, giving the team a couple days to implement a fix. But to pull a phrase from recent mission reports, the outcome of the freeze is "non-deterministic." That means sometimes the processor will still accept a reboot command; other times, it won't. It's similar to the way you deal with a frozen computer: You can try to struggle past sluggish menus and click reboot, but sometimes, your only recourse is pressing the power button.
• May 21, 2015: All systems continue to look healthy. There have been nine ground station passes over Cal Poly San Luis Obispo and Georgia Tech, with a total of 55 beacon packets downloaded thus far. These packets contain vital information on the health of the spacecraft. Regular data trends are beginning to develop as more information is downlinked. 35)
• May 20, 2015 (23:19 UTC): The Planetary Society's LightSail spacecraft is sending home telemetry data following a Wednesday commute to orbit aboard a United Launch Alliance Atlas V rocket. Deployment from the Centaur upper stage occurred at 17:05 UTC, and LightSail crossed into range of its Cal Poly San Luis Obispo ground station at 18:20 UTC). With the LightSail team on console, The Planetary Society staff gathered in Cocoa Beach, Florida to listen in as the first signals were received from space. 36)
The LightSail mission will test the critical functions of LightSail-A, a precursor to a second mission, LightSail-B, slated for 2016. That second flight will mark the first controlled, Earth-orbit solar sail flight and ride along with the first operational launch of SpaceX's Falcon Heavy rocket. 37)
The team behind The Planetary Society's LightSail spacecraft is kicking off a series of simulations to ensure the spacecraft's ground systems are ready for launch. LightSail's 30-day mission, which starts with a May 20 launch from Cape Canaveral, will be condensed into two virtual checkouts scheduled to take place during the next three weeks. This will tidy up the spacecraft's final sequence of events—a playbook that defines every mission milestone from deployment to atmospheric reentry. 38)
These simulations are part of LightSail's ORT (Operational Readiness Testing). ORT-1, the first virtual mission test, is scheduled for this week. Teams at the spacecraft's two ground stations, Cal Poly, San Luis Obispo and Georgia Tech, will run through the first two phases of the mission. The preliminary timeline for those phases is subject to change, but right now, it looks like this:
Table 3: Overview of planned/scheduled events during the LightSail mission (Ref. 38)
Figure 16: LightSail's two PSCAMS (Planetary Society Cameras) are installed at the end of the spacecraft's X-axis solar arrays. They have 2 Mpixel fisheye lenses (image credit: The Planetary Society, Jason Davis) 39)
Figure 17: Schematic view of the deployment sequence (image credit: Stellar Exploration)
The mission operations team is located at Georgia Tech (Georgia Institute of Technology) in Atlanta, GA. Primary mission control will be at CalPoly with backup at Georgia Tech.
LightSail-1 will be stored inside the Prox-1, which was developed by the Georgia Institute of Technology to demonstrate new technologies enabling two spacecraft to work in close proximity. After ejecting LightSail-1, the largely student-built Prox-1 will track and image LightSail-1, including the sail deployment.
Short history of solar sailing:
The concept of solar sailing in space—providing low-thrust spacecraft propulsion from the radiation pressure of sunlight—can be traced as far back as 1610 in a letter from Kepler to Galileo: "Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void." 40)
In the 1860s Maxwell's equations showed that light had momentum, providing a theoretical underpinning to the concept. In 1865 Jules Verne incorporated the concept in From the Earth to the Moon—perhaps the first published mention of light pushing a spacecraft through space. Further theoretical and lab-based experimental work bolstered the concept from the late 1890s through late 1920s, and for the next several decades the concept was occasionally addressed by researchers and science fiction authors. 41)
The first detailed solar sail technology and mission design effort was led by Louis Friedman at JPL starting in 1976 for a proposed 1985-86 Halley's Comet rendezvous mission. The mission concept was promoted publicly by astronomer/planetary scientist and Friedman colleague Carl Sagan, but ultimately the mission was not funded by NASA.
In 1980 Sagan, Friedman and then-JPL Director Bruce Murray formed a non-profit space advocacy organization "to inspire the people of Earth to explore other worlds, understand our own, and seek life elsewhere." The Planetary Society (TPS) is now the largest such group in the world with over 40,000 active members, and among other key objectives strives "to empower the world's citizens to advance space science and exploration.
In the early 2000s, led by Executive Director Friedman, TPS developed the Cosmos-1 solar sailing demonstration mission (Fig. 1) with primary funding from Cosmos Studios, a production company formed by Sagan's widow Ann Druyan after his passing in 1996. The spacecraft was designed, built and tested by the Babakin Science and Research Space Center in Moscow, and was intended for launch by a submarine-launched Volna rocket. A precursor in-space test of a 2-sail solar sail deployment system (vs. 8 sails for the full-up Cosmos-1 design) ended in failure in 2001 when the Volna's upper stage did not separate from its first stage. Another attempt at a full-up Cosmos-1 mission in 2005 also failed when another Volna rocket's first stage underperformed, dropping the spacecraft into the Arctic sea.
Undeterred by the Cosmos-1 mission failures, in 2009 Friedman initiated another TPS member-funded attempt at a solar sailing demo mission—actually three separate proposed missions, LightSail-1, LightSail-2 and LightSail-3—this time employing the increasingly popular 3U CubeSat design standard.
In late 2008 TPS had discussed using NASA's backup 3U CubeSat NanoSail-D2 as the first LightSail demo mission following the failed SpaceX Falcon 1 launch of NanoSail-D1 in summer 2008, but Friedman opted instead to develop a more capable solar sail system. (NanoSail-D's sail system was designed for generating atmospheric drag, not solar sailing.) NASA eventually launched NanoSail-D2 in late 2010, and after some hiccups the mission was ultimately deemed a success in late January 2011. 42)
Friedman's original LightSail program plan (mid-2009) baselined the LightSail-1 mission as the first ever to demonstrate solar sailing in Earth orbit, and this spacecraft was projected to be launch-ready by the end of 2010. The LightSail-2 mission would demonstrate an Earth-escape mission profile, while the LightSail-3 craft would ".... take us on a mission for which a solar sail spacecraft is uniquely suited: creating a solar weather monitor to provide early warning of solar storms that could affect Earth." (NASA's Sunjammer mission concept, canceled in 2014 after a years-long development effort before a targeted 2015 launch, addressed the LightSail-3 primary mission objective with a 37 x larger solar sail area.)
In 2009 TPS tapped Stellar Exploration Inc. (then located in San Luis Obispo, California, and later in Moffett Field, California) for the LightSail spacecraft design and construction effort. For several reasons, the scope of the effort was scaled back first from three spacecraft to one, and eventually back up to two. By the end of 2011 Stellar had largely completed the development and assembly of both LightSail 3U CubeSat spacecraft (later named LightSail-A and LightSail-B) and had conducted various subsystem- and system-level tests on them, though more so on LightSail-A than on LightSail-B. 43)
Meanwhile, in May 2010 the Japanese space agency JAXA launched a mission to Venus with a secondary payload called IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), a dedicated solar sail demonstration spacecraft. Three weeks after launch IKAROS was successfully separated from its piggyback ride and became the first-ever solar sailing demonstrator. The project's very successful primary mission continued through most of 2010, and even today (2015) its mission controllers establish intermittent communications. Solar sailing missions feature prominently in JAXA's long-range plans for solar system exploration.
In September 2010, long-time TPS member and then-TPS Vice-President Bill Nye (The Science Guy®, Figure 18) became the society's Executive Director following the retirement of Friedman. In February 2011 a launch opportunity for one of the LightSails materialized when the team was competitively awarded a no-charge secondary launch via NASA's Educational Launch of Nanosatellites (ELaNa) program, a key element of the agency's CubeSat Launch Initiative. 44) TPS had requested a minimum orbit altitude of 800 km to enable the solar sailing demonstration, and NASA agreed to seek such an opportunity.
Figure 18: Bill Nye with a full-scale engineering model mockup of the LightSail 3U CubeSat developed by Stellar Exploration, Inc. (image credit: LightSail Team)
Stellar continued to make progress testing the spacecraft (mostly LightSail-A) and managed to get it through several sail deployment tests and an approximation of a mission-sequence test. But in May 2012 for a variety of programmatic reasons, including the lack of firm near-term launch opportunity to 800 km (NASA had only identified two other opportunities going to half this altitude, and thus unsuitable for solar sailing), Nye put a pause on the LightSail effort and both spacecraft were placed in storage.
TPS actually investigated selling the two LightSail craft to another interested company or organization, giving them to a NASA center to support R&D and training efforts, and even donating them to a museum.
TPS member interest in the program remained high, however, so in August 2012 the society assembled a panel of experienced space technologists and space-mission managers to assess and review the program and make recommendations about whether the program should be resumed. This panel, led by Northrop Grumman Space Technology President and TPS Board member Alexis Livanos, advised to restart the effort, given certain assumptions and constraints. - During the following twelve months, several promising factors buoyed confidence in the restart recommendation:
• An excellent candidate launch opportunity for the second LightSail spacecraft was identified with the promise of a higher orbit altitude: have it serve as a target for a new mission called Prox-1, funded by the USAF UNP (University Nanosatellite Program) and defined and managed by the Center for Space Systems at the Georgia Institute of Technology (Georgia Tech).
• Given the Prox-1 opportunity, both launch opportunities identified by NASA to the lower orbits now looked promising, because such a mission could still serve as a risk-reduction exercise, demonstrating the critical solar sail deployment system (much like the first attempted Cosmos-1 demo mission) and validating the overall spacecraft design and functionality.
• A new CubeSat-focused space-technology firm had been formed in collaboration with Cal Poly (California Polytechnic University), San Luis Obispo, Tyvak Nanosatellite Systems, which had licensed and improved several key Cal Poly subsystems incorporated into the LightSail spacecraft design.
• Interest in employing CubeSats for deep-space and planetary missions was rising, especially at NASA.
• Support for LightSail by members and donors of TPS continued to be strong, in spite of the program pause.
During this period, a new program management team was identified. The overall LightSail Program Manager for TPS would be independent consultant Doug Stetson, an experienced ex-JPL mission designer, advanced technology planner and planetary program analyst. The overall LightSail Mission Director would be Georgia Tech Professor of the Practice Dave Spencer, an ex-JPL Mars mission manager and mission engineer, Director of Georgia Tech's Center for Space Systems and Principal Investigator and Mission Manager for Prox-1.
Extensive meetings during the summer of 2013 involving Stetson, Spencer and TPS as well as Stellar, Cal Poly, NASA and others resulted in considerable refinement of the program plan: 45)
• Overall program objectives were defined, with distinct mission objectives for LightSail-A and -B. (LightSail-A would take whichever ELaNa launch opportunity was ultimately selected, while LightSail-B would ride with Prox-1.)
• A requirements-verification matrix was established for the overall mission, spacecraft system and ground system.
• The overall concept for mission operations (CONOPS) and mission timelines were defined, with potential de-scopes and simplifications.
• Spacecraft technical resources budgets (mass, power, component temperature limits) were updated.
• Attitude disturbance torques and orbit decay estimates were refined for LightSail-A.
• The launch environment for LightSail A was characterized and implications to the spacecraft design were characterized.
• A baseline integration and testing plan for LightSail-A was developed.
• A trade study for possible upgrades to the flight processor and radio was conducted.
All of this progress led to a decision at a Program Assessment Review in August 2013 to formally restart the LightSail program. By the time a Midterm Program Review was held in December 2013 the reformulated program plan had come into focus: 46)
• LightSail-A, would be couched as a risk-reducing tech demo mission; LightSail-B, would be a full-up solar sailing demo mission.
• Stellar Inc. would continue in its role as lead spacecraft system contractor, augmented by space avionics and sensor systems firm Ecliptic Enterprises Corporation of Pasadena, who in turn would also have Boreal Space (Hayward, CA) and Half Band Technologies as support contractors, with Tyvak on call as needed.
• Cal Poly would develop the baseline ground operations system and lead mission operations for LightSail-A, while Georgia Tech would serve as the backup from their Center for Space Systems facility; for LightSail-B, these roles would reverse.
• Cal Poly would provide selected staff and students of its environmental test facilities to the program, and would also lead the CubeSat integration effort with the "P-POD" CubeSat carrier/deployer system and coordinate other selected launch approval activities.
• TPS would provide program funding and coordinate all outreach and media interactions.
When the decision was made to resume the program in the fall of 2013, the baseline date for having the LightSail-A spacecraft integration and testing complete and ready for shipment to the launch site was May 2014 — a very aggressive schedule. By December NASA had moved this date to the right by ~6 months to December 2014. The best estimate for the Prox-1/LightSail-B launch date was August 2015.
The LightSail-A integration and testing effort got started in earnest in the fall of 2013 at Stellar; by spring 2014, Ecliptic was assigned lead responsibility for the effort, supported by Boreal Space and Half Band. Stellar and Tyvak continued to assist the effort on contract through the fall of 2014, and then were consulted occasionally until the end of the LightSail-A mission in mid-2015.
LightSail-B Mission of TPS
The orbit for LightSail-B will allow for a full-up solar sailing demonstration. The spacecraft will ride to a 720 km circular Earth orbit inside a P-POD, which in turn will be integrated inside the Prox-1 spacecraft. The entire Prox-1 payload rides to orbit attached to an ESPA [EELV (Evolved Expendable Launch Vehicle)] ring port; the ESPA ring, in turn, is part of a cluster of payloads scheduled for a 2016 USAF-sponsored Falcon Heavy launch from Cape Canaveral,Florida (Ref. 40).
• Ride unpowered to orbit inside the Prox-1 P-POD
• Remain inert inside P-POD for ~1 week during Prox-1 initial mission operations
• Eject from P-POD; Prox-1 follows for ~2 weeks
• Power ON and boot up computer
• Activate ADCS; initiate rate damping (detumbling)
• Deploy RF antenna; start transmitting data packets
• Conduct spacecraft health and status assessment
• Wait for Prox-1 approach and rendezvous (~1 week)
• Serve as target for Prox-1 proximity operations for ~1 week, after which Prox-1 conducts stand-off observations of LightSail-B deployments
• Test ADCS subsystem and onboard cameras
• Deploy solar panels
• Deploy solar sails while imaging entire sequence
• Downlink images; assess deployed sail characteristics; Prox-1 attempts to follow
• Assess overall spacecraft status
• Go separate way from Prox-1; begin solar sailing demo (~3-5 months?)
• Conduct extended mission objectives (if possible)
The joint Prox-1/LightSail-B mission sequence is expected to last ~6 weeks from P-POD ejection. The LightSail B-only portion of the mission, during which the solar sailing demonstration will occur, is expected to last 3-6 months — or more if spacecraft health supports extended mission operations.
Figure 19: Illustration of the LightSail-B nanosatellite (left) shortly after ejection from the Prox-1 spacecraft (TPS, LightSail Team)
Note: The Prox-1 mission will demonstrate automated trajectory control for on-orbit inspection of a deployed CubeSat. The Prox-1 microsatellite has been designed and developed, fabricated and tested by a team of Georgia Tech undergraduate and graduate students who will also be responsible for mission operations. The 50 kg Prox-1 spacecraft will deploy a 3U CubeSat, namely the LightSail-B solar sail spacecraft of The Planetary Society. 47)
Prox-1 will fly in close proximity to LightSail-B (50-150 m), demonstrating automated trajectory control based upon relative orbit determination using infrared imaging. Visible images of the LightSail-B solar sail deployment event will be acquired and downlinked by Prox-1. The Prox-1 mission will also provide first-time flight validation of advanced sun sensor technology, a small satellite propulsion system, and a low-mass thermal imager. The mission is funded by the Air Force Office of Scientific Research, through the UMP (University Nanosatellite Program).
Figure 20: Baseline LightSail-B mission plan in conjunction with the Prox-1 mission (image credit TPS, LightSail Team)
2) Jim Cantrell, Louis Friedman, "LightSail-A- Flying on Light for Less," Proceedings of the 2nd ISSS (International Symposium on Solar Sailing, New York, NY, July 20-22, 2010, URL: http://www.citytech.cuny.edu/isss2010/presentations/2010July20/Cantrell_Lightsail-1.ppsx
3) John Antczak, "After letdown, solar-sail project rises again," Nov. 9, 2009, URL: http://rss.msnbc.msn.com/id/33812469/ns/technology_and_science-space/
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6) XChris Biddy, "LightSail-1™ Solar Sail Design and Qualification," 41st Aerospace Mechanism Symposium, Pasadena, CA, USA, May 18.20, 2012, URL: http://www.planetary.org/explore/projects/lightsail-solar-sailing/Aerospace-Mechanisms-Symposium_Chris-Biddy.pdf
8) Bill Nye, "LightSail: A Revolutionary Solar Sailing Spacecraft," URL: https://www.kickstarter.com/projects/theplanetarysociety/lightsail-a-revolutionary-solar-sailing-spacecraft/video_share
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15) Jason Davis, "LightSail update: Launch dates," The Planetary Society, July 10, 2014, URL: http://www.planetary.org/blogs/jason-davis/2014/lightsail-update-launch.html
16) Louis Friedman, Bruce Betts, Chris Biddy, James Cabtrell, Alex Diaz, Matthew Negrenz, David Spencer, Thomas Svitek, "LightSail: Spacecraft ready for launch," Proceedings of the 63rd IAC (International Astronautical Congress), Naples, Italy, Oct. 1-5, 2012
17) Stephanie Schierholz, Jason Davis, Loretta DeSio, "NASA's CubeSat Initiative Aids in Testing of Technology for Solar Sails in Space," NASA, May 20, 2015, Release 15-101, URL: http://www.nasa.gov/press-release/nasa-s-cubesat-initiative-aids-in-testing-of-technology-for-solar-sails-in-space
18) Stephanie Schierholz, Tracy McMahan, "NASA Test Materials to Fly on Air Force Space Plane," NASA, May 6, 2015, Release 15-081, URL: http://www.nasa.gov/press-release/nasa-test-materials-to-fly-on-air-force-space-plane
19) Patrick Blau, "AFSPC-05 Secondary Payloads," Spaceflight 101, URL: http://www.spaceflight101.com/afspc-05-secondary-payloads.html
20) "ELaNa XI CubeSat Launch on AFSPC-5," NASA, May 2015, URL: http://www.nasa.gov/sites/default/files/files/ELaNa-XI-Factsheet-508.pdf
21) "Atlas V AFSPC-5: ULTRASat CubeSat Summary," URL: http://www.ulalaunch.com/uploads/docs/Launch/AtlasV_AFSPC-5_ULTRASat_CubeSat_descriptions.pdf
22) Christopher Dinelli, Samudra Haque, Jin Hang, Michael Keidar, Kristen Castonguay,"Ballistic Reinforced Communication Satellite (BRICSat-P): The First Flight of an Electric Micropropulsion System for CubeSat Mission Applications," Proceedings of iCubeSat 2014, 3rd Interplanetary CubeSat Workshop, Pasadena, CA, USA, May 27-28, 2014, URL: https://icubesat.files.wordpress.com/2014/05/icubesat-org_2014_b-2-4-bricsat-p_dinellie_201405281748.pdf
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43) Chris Biddy, "LightSail-1 Solar Sail Design and Qualification," 41st Aerospace Mechanism Symposium, NASA/JPL, Pasadena, CA, May 16-18, 2012, URL: http://www.planetary.org/explore/projects/lightsail-solar-sailing/Aerospace-Mechanisms-Symposium_Chris-Biddy.pdf
44) Stephanie Schierholz, Jason Davis, Loretta DeSio, "NASA's CubeSat Initiative Aids in Testing of Technology for Solar Sails in Space," NASA, Release 15-101, May 20, 2015, URL: http://www.nasa.gov/press-release/nasa-s-cubesat-initiative-aids-in-testing-of-technology-for-solar-sails-in-space
45) Doud Stetson, ""LightSail Program Assessment Review," PowerPoint chart deck, The Planetary Society. Review held at The Planetary Society's headquarters in Pasadena, CA, August 29, 2013
46) LightSail Team, "LightSail Program Midterm Review," PowerPoint chart deck. Review held at Stellar Exploration Inc.'s facility in Moffett Field, California, Dec. 16, 2013
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).